Kinetic energy impact less-lethal projectiles have been in use for over 30 years. The early less-lethal projectiles were square cloth bags or sacks filled with No. 9 lead shot. There were two sizes, a 12-ga. Shotgun round containing 40 grams of lead shot and a 37 mm size containing 150 grams of lead shot. These projectiles were fired at a muzzle velocity of 230 and 300 feet per second (fps), for the shotgun, and from 110 to 250 feet per second (depending on the range) for the 37 mm rounds. The muzzle kinetic energy was about 70 and 120 ft-lbs, for the shotgun and from 70 to over 320 ft-lbs for the 37 mm projectiles.
These projectiles were widely used by the law enforcement community after it was demonstrated by experiment that the energy delivered by the impact was below the level determined to be lethal by blunt trauma impact to the heart area. The bags were rolled up inside the shotshell of the 12 ga. Shotgun, and they unroll at about 20 feet from the muzzle. When the bags impacted at less than the unrolling distance, the area of contact was reduced to less than 1 inch, thus raising the energy per unit area to the point where the bag would penetrate into the body causing serious damage.
In the late 1990 a new form of bag was introduced. The “sock bag” as it became known, was fabricated from a coarsely woven fabric in the shape of a tube, hence the name, and filled with # 9 lead shot and tied with a string to form the bag leaving a tail to act as an stabilizer. These bags suffered from the same problem as the rolled-up square bags, when impacting at 20 feet range, the kinetic energy density was about 220 ft-lbs/square inch with some expansion and if fully expanded the kinetic energy density was about 160 ft-lbs/sq in. when launched at 300 fps. In comparison a square bag at the same velocity would have a kinetic energy density of about 66 ft-lbs/sq in, when fully expanded and launched at 300 fps. The kinetic energy density goes up to over 230 ft-lbs/sq. in. when the bag strikes the target while still rolled up.
A subsequent development introduced a foam projectile fired from a 40 mm launcher. This design abandoned the 12 gauge size in favor of the larger diameter impact area available from the larger diameter projectiles. The increased area of impact lowers the energy density and the compression of the foam nose lowers the sharpness of the impulse transmitted to the target individual at impact. A sharp impulse is more deleterious to tissue than a softer one.